Another fun one I've gotten bitten by a lot is that the /etc/cron.* directories are run sequentially, so if someone who doesn't know this put some long running process in it, ideally with a name that sorts first, it blocks everything else in that directory. (I personally know this, obviously, since I'm saying it now, but I've been bitten by the other people who do not realize this and do not think about how putting a process that may run for three hours at the beginning of cron.hourly means that the other processes may not run for that long.)